Known in the past has been an internal combustion engine which arranges an NOx adsorbent for adsorbing NOx in exhaust gas and an NOx purifying catalyst for purifying NOx in the exhaust gas in an engine exhaust passage. In this internal combustion engine, the NOx in the exhaust gas is adsorbed at the NOx adsorbent from when engine operation has started to when the temperature of the NOx purifying catalyst reaches the activation temperature, therefore the release of NOx into the atmosphere is suppressed.
In this regard, while engine operation is suspended, the gas which is present in the engine exhaust passage contains moisture. This moisture is adsorbed at the NOx adsorbent before the engine is restarted. As a result, when the engine is restarted, the quantity of NOx which the NOx adsorbent can adsorb is reduced by the quantity of moisture which is adsorbed at the NOx adsorbent. That is, before the temperature of the NOx purifying catalyst reaches the activation temperature, the quantity of NOx which is released into the atmosphere is liable to increase by the quantity of moisture which is adsorbed at the NOx adsorbent.
Therefore, known has been an internal combustion engine which attaches an electric heater to an NOx adsorbent, calculates a quantity of moisture which is adsorbed at the NOx adsorbent, operates the electric heater to raise the temperature of the NOx adsorbent when the quantity of adsorbed moisture exceeds a threshold quantity, and thereby makes the NOx adsorbent release the moisture (see PLT 1).